Temperature sensing mechanism



March 8, 1966 D. s 3,239,634

TEMPERATURE SENSING MECHANISM Filed May 22, 1963 INVENTOR. P056670 l/AMS United States Patent 3,239,634 TEMPERATURE SENSING MECHANISM Robert D.-Iiams, 2011 S. Dixie Ave., Dayton 9, Ohio Filed May 22, 1963, Ser. No. 282,505 7 Claims. (Cl. 200-142) formation and, in conjunction therewith, a mechanism to sense the softening of the thermoplastic substance and effect appropriate temperature controls. The thermoplastic substance used is typically formed into theshape approximately of a tetrahedron and is known inthe trade as a pyrometric cone.

Due to the high temperatures reached within the kiln, it. is found impractical to place the mechanism which senses the softening of the pyrometric cone entirely inside the kiln. Thus, for many applications, the kiln is heated electrically and the sensing mechanism is utilized to effect a switching function, so as to control the supply of electrical power to the kiln. For reliability of operation, it

is desirable to locate the electrical components of the sensing mechanism outside the kiln, the information that the cone has softened being relayed mechanically through the wall of the kiln. In prior art devices, the problems most frequently encountered concern the mechanism by which the information is relayed through the wallof the kiln.

An object of the present invention is to provide an improved mechanism for sensing the softening of a pyrometric cone and relaying this information through the wall of a kiln.

Another object of the present invention is to provide a mechanism for sensing the softening of a pyrometric cone in a kiln which utilizes a rotary movement to relay this information to the exteriorof the kiln. By using a rotary movement to relay information concerning the softened condition of the pyrometric cone through the wall of the kiln, it is possible to assemble the temperature control mechanism on the kiln with a minimum of disturbance to the insulating walls of the kiln and a minimum of heat loss resulting therefrom.

Another object of the present invention is to provide an improved means for supporting a pyrometric cone in a kiln or. the like, so as to enable detection of the softening thereof.

Other objects and advantages reside in the construction of parts, the combination thereof, the method of manufacture and the mode of operation, as will become more apparent from the following description.

In the drawing, FIGURE 1 is a perspective view of the temperature control assembly embodying the present invention, a portion having been broken away to reveal interior detail.

FIGURE 2 is a fragmentary, perspective view, illustrating the manner in which the mechanism of FIGURE 1 supports a pyrometric cone.

FIGURE 3 is a fragmentary, perspective view analogous to FIGURE 2, illustrating the condition of the support for the pyrometric cone after softening of the cone.

FIGURE 4 is an enlarged, fragmentary, sectional view, taken substantially along the line 44 of FIGURE 1.

FIGURE 5 is a sectional view analogous to FIGURE 4,

ice

but showing adifferent operating position for the mechanism disclosed therein.

Referring tothe drawing in greater detail, the control mechanism of the present invention is illustrated as housed in a suitable housing 10 having a forward wall 11 framed on opposite sides thereof by flanges 12 and 14. Theflanges Hand 14 are provided with apertures 16 .adapted to receive suitable fasteners for attaching the housing to an external wall of a kiln or oven.

For assembly of the temperature control mechanism onto .thekiln, twospaced holes or borings, which may be relatively small in diameter, are required in the wall of the kiln. One of these. borings receives a horizontally disposed rod or shaft .18 fixedly attached to the rear wall 20 .ofJthe housing and adapted to project through a suitable aperture in .the front wall 11 into the interior of the kiln. Attachment to the rear wall 20 is provided by means .of a collar.23 secured rigidly to the rod 18 which is drawn against the rear wall 20 by means of a threaded nut 22, as shown.

'The other of the borings in the wall of the kiln re- .ceives a shaft 24 which supports mechanism for sensing the softening of a pyrometric cone. Bushings 26 and 28 mounted in the front and rear housing walls, respectively, support the shaft'24 for rotation relative to the housing 10. The shaft 24 is secured against axial movement relative to the housing by means of collars, one of which is shown at 30 and the other of which is obscured by the bushing 28.

A torsional bias is applied to the shaft 24 by means of an eccentric weight 32 secured to the shaft within the interior of the housing 10. This torsional bias is applied to a pyrometric cone in the following fashion. The shaft '24 is bent at its outer end, so as to have a reentrant portion 36, then is bent forwardly, so as to have an angularly disposed arm or hook 38. As shown in FIGURE 1,

"the shafts 18 and24 occupy substantially a common horizontal plane and are spaced apart in said plane. As shown in FIGURE 2, the'spacing of said shafts is such as to provide support for a pyrometric cone 40, one end of which rests on the shaft 18 and the other end of which rests on the reentrant portion 36 of the shaft 24. The eccentric weight 32 which applies a torsional bias to the shaft 24 is so positioned thatthe hook38 formed on the outer end of the shaft 24 is urged in a clockwise direction, as illustrated in FIGURE 2, against the upper surface of the cone 40, thereby clamping the cone against both shafts 18 and 24. In order to accommodate varying sizes and shapes of pyrometric elements, the weight 32 is releasably secured to the shaft 24 by means of an adjustment screw 34, this screw enabling adjustment of the angular position of the weight 32 relative to the hook 38. In operation-,it is apparent that when the cone 40 has been subjected to a temperature high enough to cause softening thereof, the cone will be incapable of resisting thepressure applied thereto which results from the action of gravity on the weight 32. Accordingly, the shaft 24will be rotated in a counterclockwise direction, causing a' deformation of the cone 40, as shown in FIGURE 3.

The rotation of the shaft 24, permitted by a softening of the cone 40, is caused to actuate a temperature control system in the following manner. Mounted upon the weight 32 by means of a bracket 44 and screw 46 is a mercury switch comprising a capsule 42 containing a quantity of mercury 48. Entering one end of the capsule 42'are two wires from a conductor 50. When these two Wires are submerged in the mercury, the mercury provides a current carrying contact between the two wires.

During times when the cone 40 is a rigid body, i.e., at temperatures lower than the critical temperature, the mercury switch occupies the position illustrated in FIGURE 4, wherein the two wire elements are submerged in mercury.

When the critical temperature has been reached, the weight 32 rotates under the force of gravity to a vertical position, as shown in FIGURE 5, wherein the wires of the conductor 50 are elevated above the mercury level and the contact between the two wires is broken.

In a typical application, the two wires in the conductor 50 represent one leg of the power supply to heating coils disposed within the kiln. When these wires are submerged in the mercury, as shown in FIGURE 4, the supply of electrical power to the heating coils is completed by the mercury. As soon as the cone 40 softens, however, the weight 32 rotates to the vertical position shown in FIG- URE 5, interrupting the supply of power to the heating coils.

In describing this simple control circuit, it is not intended to limit the application of the present sensing mechanism to such circuitry. Thus, it will be understood by those skilled in the art that, where desired, the conductor 50 might be part of a low current relay circuit, which would be used to control a higher current supplied to the heating coils. Still other variations will occur to those skilled in the art.

It will also be recognized that the mercury switch disclosed, which depends for its operation upon its orientation in a gravitational field, can be replaced by other types of switches, such as micro-switches which would rely on a positive pressure delivered by the weight 32, without departing from the spirit of the present invention. Further, it will be obvious that the weight 32, which responds to gravitational forces, can be replaced in its function by another conventional element for applying a torsional bias, such as a spring.

In the operation of the present temperature control mechanism, it will be noted that the only movement required to signify softening of the pyrometric cone is a rotary motion about the axis of the boring in the wall of the kiln which receives the shaft 24. Accordingly, this opening need be no larger than the diameter of the shaft 24, which, in turn, need be only large enough to withstand the torsional forces applied thereto by the eccentric Weight 32. Consequently, the present heat control mechanism may be attached to a kiln with a minimum of disturbance to the walls of the kiln, the attachment requiring only two borings which may be exceedingly small in diameter. By minimizing the disturbance to the walls of the kiln, heat losses are minimized and it will be appreciated by those skilled in the art that the small diameter of the shafts 18 and 24 permitted by the present invention also minimizes heat losses due to conduction of heat energy in the shafts 18 and 24.

Although the preferred embodiment of the device has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

1. A device for sensing the softening of a thermoplastic body within a heating chamber having an aperture in one wall thereof and for actuating a control system external to said chamber in response to softening of said thermoplastic body, there being means in said chamber to brace said body, said device comprising a shaft adapted to pass through said aperture whereby an inner end of said shaft projects into said chamber and an outer end thereof projects out of said chamber, means supporting said shaft for rotation about its longitudinal axis, said shaft being rotatable about said axis between first and second positions, means biasing said shaft to said second position, said shaft supporting at the inner end thereof hook means adapted to engage said body in said first position, said bias means upon engagement of said body by said hook means being adapted to press said body aganst said brace means whereby said body resists rotation of said shaft to said second position until softening of said body renders same incapable of such resistance, and means supported by the outer end of said shaft responding to movement of said shaft to said second position for actuating said control system.

2. The device according to claim 1, wherein said bias means comprises a weight supported by said shaft and disposed eccentric to the axis of said shaft, said weight responding to the force of gravity to apply a torsional bias to said shaft.

3. The device according to claim 1, wherein the means for actuating said control system comprises a gravity sensitive electrical switch element fixedly mounted with respect to the outer end of said shaft, the rotation of said shaft between said first and second positions changing the orientation of said switch element with respect to the earths gravitational field to effect a switching action.

4. The device according to claim 1, wherein the means supporting said shaft comprises a housing adapted for attachment to said one wall of said chamber.

5. A device for sensing the softening of a thermoplastic body within a chamber having spaced apertures in one wall thereof and for actuating a control system external to said chamber in response to softening of said thermoplastic body, said device comprising a shaft adaptedto pass through one of said apertures whereby an inner end of said shaft projects into said chamber and an outer end thereof projects outside of said chamber, housing means engaging and supporting said outer end of said shaft for rotation about its longitudinal axis, said shaft being rotatable about said axis between first and second positions, means biasing said shaft to said second position, a brace member adapted to pass through the other of said apertures, said brace member having an inner end adapted to project into said chamber, said housing means supporting the outer end of said brace member in fixed spaced relation to the axis of said shaft, said shaft supporting at the inner end thereof hook means adapted to engage said body in said first position, said bias means upon engagement of said body by said hook means being adapted to press said body against said brace whereby said body resists rotation of said shaft to said second position until softening of said body renders same incapable of such resistance, and means supported by the outer end of said shaft responding to movement of said shaft to said second position for actuating said control system.

6. The device according to claim 5, wherein said shaft and said brace member are disposed in spaced relation and are adapted to cooperatively support opposite ends of said thermoplastic body, said bias means rotating said shaft so as to cause the hook means supported thereby to engage and press said thermoplastic body against said shaft and said brace member, the space between said shaft and said brace member permitting said hook means to pass therebetween upon softening of said thermoplastic body.

7. A device for sensing the softening of a thermoplastic body within a chamber having spaced apertures in one wall thereof and for actuating acontrol system external to said chamber in response to softening of said thermoplastic body, said device comprising a housing adapted to be fixed to the exterior of said one wall, a shaft adapted to pass through one of said apertures whereby an inner end of said shaft projects into said chamber and an outer end thereof projects into said housing, means supporting said shaft for rotation relative to said housing and about its longitudinal axis, said shaft being rotatable about said axis betwen first and second positions, means disposed within said housing engaging said shaft and biasing said shaft rotationally to said second position, an elongate brace member adapted to pass through the other aperture in said one wall, said housing supporting said brace member in spaced parallel relation to said shaft, said shaft supporting adjacent the inner end thereof a radially disposed hook member the radial extent of which relative to said axis is smaller than the spacing between said shaft and said brace member, said shaft and said brace member being adapted to engage and support opposite ends of said thermoplastic body, said bias means rotating said shaft so as to bring said hook member into engagement with the thermoplastic body when supported between said shaft and said brace member and thereby press said thermoplastic body against said shaft and said brace member, said thermoplastic body resisting rotation of said shaft to said second position until softening of said body renders same References Cited by the Examiner UNITED STATES PATENTS 6/1951 Strange 200142 4/1954 Dawson 73358 X LOUIS R. PRINCE, Primary Examiner. 

1. A DEVICE FOR SENSING THE SOFTENING OF A THERMOPLASTIC BODY HAVING A HEATING CHAMBER HAVING AN APERTURE IN ONE WALL THEREOF AND FOR ACTUATING A CONTROL SYSTEM EXTERNAL TO SAID CHAMBER IN RESPONSE TO SOFTENING OF SAID THERMOPLASTIC BODY, THERE BEING MEANS IN SAID CHAMBER TO BRACE SAID BODY, SAID DEVICE COMPRISING A SHAFT ADAPTED TO PASS THROUGH SAID APERTURE WHEREBY AN INNER END OF SAID SHAFT PROJECTS INTO SAID CHAMBER AND AN OUTER END THEREOF PROJECTS OUT OF SAID CHAMBER, MEANS SUPPORTING SAID SHAFT FOR ROTATION ABOUT ITS LONGITUDINAL AXIS, SAID SHAFT BEING ROTATABLE ABOUT SAID AXIS BETWEEN FIRST AND SECOND POSITIONS, MEANS BIASING SAID SHAFT TO SAID SECOND POSITION, SAID SHAFT SUPPORTING AT THE INNER END THEREOF HOOK MEANS ADAPTED TO ENGAGE SAID BODY IN SAID FIRST POSITION, SAID BIAS MEANS UPON ENGAGEMENT OF SAID BODY BY SAID HOOK MEANS BEING ADAPTED TO PRESS SAID BODY AGAINST SAID BRACE MEANS WHEREBY SAID BODY RESISTS ROTATION OF SAID SHAFT TO SAID SECOND POSITION UNTIL SOFTENING OF SAID BODY RENDERS SAME INCAPABLE OF SUCH RESISTANCE, AND MEANS SUPPORTED BY THE OUTER END OF SAID SHAFT RESPONDING TO MOVEMENT OF SAID SHAFT TO SAID SECOND POSITION FOR ACTUATING SAID CONTROL SYSTEM.
 3. THE DEVICE ACCORDING TO CLAIM 1, WHEREIN THE MEANS FOR ACTUATING SAID CONTROL SYSTEM COMPRISES A GRAVITY SENSITIVE ELECTRICAL SWITCH ELEMENT FIXEDLY MOUNTED WITH RESPECT TO THE OUTER END OF SAID SHAFT, THE ROTATION OF SAID SHAFT BETWEEN SAID FIRST AND SECOND POSITIONS CHANGING THE ORIENTATION OF SAID SWITCH ELEMENT WITH RESPECT TO THE EARTH''S GRAVITATIONAL FIELD TO EFFECT A SWITCHING ACTION. 